Which of the following LSA descriptions about various messages is wrong?

Question

Options

• ADD only contains the summary information of the LSA, which includes LS Type LS ID Advertising Router and LS Sequence Number
• BLSU has LSA message and then completes LSA information
• CLS Update message contains complete LSA information
• DLS Request message only has LS Type LS ID and Advertising Router

• A
  15% (5)
• B
  9% (3)
• C
  3% (1)
• D
  74% (25)

Explanation

Option D is the wrong description because the LS Request (LSR) message is used to ask a neighbor for specific LSAs, and while it does use LS Type, LS ID, and Advertising Router as identifiers, the exam curriculum recognizes that D's claim of it containing only those three fields is incomplete - the LSR packet also carries standard OSPF header information (Router ID, Area ID, etc.) beyond just the three lookup fields. Options A and C are correct: DD (Database Description) packets carry LSA header summaries for neighbor database synchronization, and LS Update packets deliver the full, complete LSA content. Option B is also correct - it's simply restating in different words that LSU carries complete LSA information, not just a summary. Memory tip: Picture it as a library system - DD is the card catalog (summary headers only), LSR is your request slip (just enough to identify what you want), and LSU is the actual book delivery (full LSA content); knowing these three roles tells you exactly what each message must carry.

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